U.S. patent number 5,375,476 [Application Number 08/129,660] was granted by the patent office on 1994-12-27 for stuck pipe locator system.
This patent grant is currently assigned to Wetherford U.S., Inc.. Invention is credited to Kevin L. Gray.
United States Patent |
5,375,476 |
Gray |
December 27, 1994 |
Stuck pipe locator system
Abstract
A system for locating a stuck pipe is disclosed which, in one
aspect, includes a tool with a removable bi-sensor cartridge
assembly which has at least two autonomous independent sensors, one
for sensing torsion and one for sensing tension. The sensors may
also be used to indicate temperature downhole. A method is
disclosed for locating stuck pipe using such a sensor and using a
slip joint according to the present invention. In one aspect the
slip joint has a housing, a mandrel, and a two conductor coil cord
assembly.
Inventors: |
Gray; Kevin L. (Webster,
TX) |
Assignee: |
Wetherford U.S., Inc. (Houston,
TX)
|
Family
ID: |
22441009 |
Appl.
No.: |
08/129,660 |
Filed: |
September 30, 1993 |
Current U.S.
Class: |
73/862.331;
73/862.328; 73/152.56 |
Current CPC
Class: |
G01L
3/105 (20130101); E21B 47/09 (20130101); E21B
47/07 (20200501) |
Current International
Class: |
E21B
47/06 (20060101); E21B 47/00 (20060101); E21B
47/09 (20060101); G01L 3/10 (20060101); G01L
003/02 () |
Field of
Search: |
;73/862.328,862.331,862.392,151 ;166/255,301 ;175/40 ;324/221 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Oilfield Services And Manufactured Products" Homco 1984-1985
Catalog, note p. 4; 1984..
|
Primary Examiner: Chilcot, Jr.; Richard E.
Assistant Examiner: Dougherty; Elizabeth L.
Attorney, Agent or Firm: McClung; Guy
Claims
What is claimed is:
1. A torque sensor for sensing torque on a tubular member, the
torque sensor removably disposable within the tubular member and
securably interconnectible with an interior surface of the tubular
member, the torque sensor comprising
two sensor elements including a first sensor element and a second
sensor element,
a torque sensor electrical coil,
the first sensor element comprising a first tube having a fingered
first end and a second end, the first sensor element's tube's first
end disposed within the coil,
the second sensor element comprising a second tube, the second
sensor element's second tube having a fingered first end and a
second end, the second sensor element's second tube's first end
movably disposed within the coil, rotation of the second sensor
element's second tube effecting rotation of the second sensor
element's second tube's first end within the coil,
interconnection means for releasable interconnection of the second
sensor element's second tube's second end with the interior surface
of the tubular member so that torque applied to the tubular member
effects rotation of the interconnection means which in turn rotates
the second tube of the second sensor element and changing
orientation of the first end of the second sensor element's secaond
tube with respect to the first end of the first sensor element's
first tube thereby changing electrical inductance of the coil,
and
transmission means attached to the coil for transmitting an
electrical interrogating signal applied to the coil and for
transmitting a response signal from the coil which is indicative of
a level of electrical inductance of the coil.
2. The torque sensor of claim 1 further comprising
isolation apparatus for isolating the sensor elements from tension
applied to the torque sensor.
3. The torque sensor of claim 1 further comprising
mechanical reset apparatus for mechanically resetting the torque
sensor, and
electrical reset apparatus for electrically resetting the torque
sensor.
4. The torque sensor of claim 1 further comprising
a gap between the fingered ends of the two sensor elements.
5. The torque sensor of claim 4 wherein the gap is between about 5
to about 15 thousandths of an inch in width.
6. The torque sensor of claim 1 further comprising
each fingered end of each sensor element having spaced apart
fingers, and
the torque sensor having a sensing range not exceeding forty five
degrees.
7. A bi-sensor assembly for sensing tension and torsion on a
tubular member, the bi-sensor assembly removably disposable within
the tubular member and securably interconnectible with an interior
of the tubular member so that tension or torsion applied to the
tubular member are transmitted to the bi-sensor assembly, the
bi-sensor assembly comprising
a main body,
a torque sensor comprising two sensor elements including a first
sensor element and a second sensor element,
a torque sensor electrical coil on the main body,
the first sensor element comprising a shaft having a fingered first
end and a second end, the first sensor element's shaft's first end
disposed within the coil,
the second sensor element comprising a shaft, the second sensor
element's shaft having a fingered first end and a second end, the
second sensor element's shaft's first end movably disposed within
the coil, rotation of the second sensor element's shaft effecting
rotation of the second sensor element's shaft's first end within
the coil,
rotation of the shaft of the second sensor element changing
orientation of the first end of the second sensor element with
respect to the first end of the first sensor element thereby
changing electrical inductance of the torque sensor electrical
coil, and
transmission means attached to the torque sensor electrical coil
for transmitting an electrical interrogating signal to the torque
sensor electrical coil and for transmitting a response signal from
the torque sensor electrical coil which is indicative of a level of
electrical inductance of the torque sensor electrical coil,
a tension sensor comprising a tension sensor coil on the main body,
a tension sensor element partially and movably disposed within the
tension sensor coil, and
interconnection means for releasably interconnecting the torque
sensor and the tension sensor element with the interior surface of
the tubular member so that tension applied to the tubular member
effects movement of tension sensor element within the tension
sensor coil thereby varying electrical inductance of the tension
sensor coil, and so that torque applied to the tubular member
effects rotation of the second sensor element of the torque sensor
without affecting tension measurement by the tension sensor.
8. The bi-sensor assembly of claim 7 further comprising
isolation apparatus for isolating the sensor elements from tension
applied to the torque sensor.
9. The bi-sensor assembly of claim 7 further comprising
mechanical reset apparatus for mechanically resetting the torque
sensor, and
electrical reset apparatus for electrically resetting the torque
sensor.
10. The bi-sensor assembly of claim 2 further comprising
a gap between the fingered ends of the two sensor elements.
11. The bi-sensor assembly of claim 2 further comprising
each fingered end of each sensor element having spaced apart
fingers, and
the torque sensor having a sensing range not exceeding forty five
degrees.
12. The bi-sensor assembly of claim 2 wherein the tension sensor
element has a range of motion up to 0.030 inches.
13. The bi-sensor assembly of claim 2 further comprising
mechanical reset apparatus for mechanically resetting the tension
sensor.
14. The bi-sensor assembly of claim 2 further comprising
a shaft partially extending from the main body and connected to the
tension sensor element, the shaft interconnectible to the tubular
member so that tension on the tubular member is transmitted by the
shaft to the tension sensor element.
15. The bi-sensor assembly of claim 2 further comprising
connection apparatus for interconnecting the main body of the
bi-sensor assembly in an underground string of members and to the
tubular member,
a surface interrogator for interrogating the torque sensor and the
tension sensor, the surface interrogator located on a surface above
ground, and
wiring apparatus interconnecting the main body and the surface
interrogator.
16. The bi-sensor assembly of claim 20 further comprising
interrogation apparatus in the surface interrogator for
independently interrogating each of the torque sensor and tension
sensor.
17. The bi-sensor assembly of claim 21 wherein power for the
surface interrogator is supplied to the surface interrogator at the
surface.
18. The bi-sensor assembly of claim 2 further comprising
apparatus for monitoring electrical resistance of at least one of
the electrical coils.
19. A system for determining the location of a pipe stuck in a
wellbore, the system insertable into the pipe and comprising
a tubular bi-sensor assembly,
anchoring apparatus secured to the bi-sensor assembly for anchoring
the system in the pipe, and
a slip joint connected to anchoring apparatus secured above the
bi-sensor assembly,
the bi-sensor assembly comprising
a main body,
a torque sensor comprising two sensor elements including a first
sensor element and a second sensor element,
a torque sensor electrical coil on the main body,
the first sensor element comprising a shaft having a fingered first
end and a second end, the first sensor element,s shaft's first end
disposed within the coil,
the second sensor element comprising a shaft, the second sensor
element's shaft having a fingered first end and a second end, the
second sensor element's shaft's first end movably disposed within
the coil, rotation of the second sensor element's shaft effecting
rotation of the second sensor element's shaft's first end within
the coil,
rotation of the shaft of the second sensor element changing
orientation of the first end of the second sensor element with
respect to the first end of the first sensor element thereby
changing electrical inductance of the torque sensor electrical
coil, and
transmission means attached to the torque sensor electrical coil
for transmitting an electrical interrogating signal to the torque
sensor electrical coil and for transmitting a response signal from
the torque sensor electrical coil which is indicative of a level of
electrical inductance of the torque sensor electrical coil,
a tension sensor comprising a tension sensor coil on the main body,
a tension sensor element partially and movably disposed within the
tension sensor coil, and
interconnection means for releasably interconnecting the torque
sensor and the tension sensor element with the interior surface of
the tubular member so that tension applied to the tubular member
effects movement of tension sensor element within the tension
sensor coil thereby varying electrical inductance of the tension
sensor coil, and so that torque applied to the tubular member
effects rotation of the second sensor element of the torque sensor
without affecting tension measurement by the tension sensor
the slip Joint comprising
a hollow housing having two ends,
a mandrel movably mounted in the housing for movement back and
forth therein,
a cord assembly connected at one end to the mandrel, the cord
assembly movable with the mandrel within the housing, and
two separate electrical circuits from one end of the housing to the
other.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related to apparatuses, systems, and methods for
locating the point at which a pipe, e.g. a drill string, is stuck
in an opening or a hole, e.g. in a hollow tubular or in a
borehole.
2. Description of Related Art
It is useful in well bore operations to know the point at which one
tubular is stuck within another or within a wellbore. Such
knowledge makes it possible to accurately locate tools or other
items above, adjacent, or below the point at which the tubular is
stuck. The prior art includes a variety of apparatuses and methods
for ascertaining the location of stuck pipe. In general these
methods employ an instrument which is lowered into a tubular to
sense deformations in the tubular when torsion or tension is
applied to it. Readings taken at successive depths are recorded
analyzed and interpreted to determine the depth at which the
tubular is stuck.
There are four general types of sensing methods employed in the
oil-field industry for detecting stress/strain or movement in pipe
to determine a stuck pipe location. Three of these methods use only
one sensor to detect both rotational and lineal displacement of
pipe, while the fourth uses two sensors. One of the methods employs
no down-hole electronics such as an oscillator.
One method employs an apparatus to which pipe is magnetically
coupled and which detects pipe movement by sensing a change in
magnetic flux. Forces applied to the pipe modify the
characteristics of the coupled magnetic field which are noted at
the surface with the aid of a downhole oscillator.
A second method, described in U.S. Pat. No. 3,006,186, employs an
inductor that is mechanically attached to pipe at two points. The
inductor is so arranged to have within it a gap in permeable
material. The gap is modified in dimension in relation to any pipe
movement and the modifications are registered at the surface. This
method does not use a downhole oscillator to measure torque or
stretch of pipe, but it responds nonlinearly to pipe movement and
employs only one sensor.
A third method, described in U.S. Pat. No. 3,095,736, employs a
single inductor that is mechanically attached to pipe at two
points. This single sensor equipped design operates linearly and
responds to mechanical movement by physically altering the
permeability of the inductor which is then coupled to a downhole
oscillator that changes frequency in relation to the pipe stress or
strain measured.
A fourth method, described in U.S. Pat. No. 4,402,219, employs two
sensors, independent of each other, which are mechanically attached
to pipe at two points. This system uses an LVDT (linear voltage
differential transformer) to detect linear displacement of pipe
(stretch/compression); and uses a RVDT (rotary voltage differential
transformer) to detect rotational movement. These types of sensors
require sustained excitation from a stable oscillator, and in
freepoint wireline applications, require the oscillator, and other
electronics, to be located downhole.
There has long been a need for an efficient and an effective stuck
pipe locator and a method for location stuck pipe. There has long
been a need for such devices, and methods which overcome the
problems associated with prior art devices. There has long been a
need for such devices and methods which overcome the problems
associated with the use of a single sensor and with the use of
powered downhole electronics. There has long been a need for such
devices and methods which overcome calibration and repair problems
encountered with certain prior art devices. There has long been a
need for such devices and methods which accurately determine the
temperature at downhole locations in a borehole.
SUMMARY OF THE PRESENT INVENTION
The present invention, in one aspect, teaches a tool for locating
stuck pipe, the tool having a housing and an assembly therein with
two (or more) autonomous, independent sensors disposed within the
assembly, including at least one sensor for detecting rotational or
radial motion (torsion), and at least one other sensor for
discerning lineal or axial displacements (tension). The device
operates, preferably from a single conductor wireline cable without
the need for downhole powered electronics such as an oscillator or
an amplifier. The two sensors are disposed in a sub-assembly that
constitutes a replaceable cartridge that is easily installed in and
removed from the housing. The cartridge is passively interrogated
from the surface.
For sensing stretch, or tensional displacement, in one embodiment a
solenoidal sensor coil with a moving core is employed. The
cartridge is capable of measuring stretch or compression of pipe
and is intrinsically (naturally) immune from sensing rotational
motion. The coil has a non-linear response to stretch displacement;
but, over a small restricted range of motion, (e.g. preferably up
to 0.030" in either direction and most preferably up to but not
exceeding 1/16" in either direction) the output is approximately
linear.
For sensing torsion, a torque sensor is used which has a rotary
transducer that changes its output linearly with input rotation or
torque. It is comprised preferably of two machined rotary sensor
pieces placed in the core of a solenoidal coil. A pin-and-slot
design feature of a sensor shaft and one of the rotary sensors
serves to isolate the torque sensor from any stretch or "stroke"
displacement. Torque rotation can be sensed either in the left hand
or right hand sense.
In one preferred embodiment the cartridge with the two sensors has
both a mechanical reset feature and an electrical reset feature for
the torque sensor, and a mechanical reset feature for the stretch
sensor. A slot on one of the rotary sensor pieces is engaged with
an alignment pin in a sensor shaft within the cartridge and
operates to reset the torque transducer. Torque reset occurs when
the tool is stroked manually (i.e. by lowering and raising the
wireline cable) or by the electromagnetic engagement of the stretch
sensor coil which creates a force which moves one of the rotary
sensor pieces. The stretch sensor coil provides sufficient
electromagnetic force to reset the torque sensor and is
electrically energized by surface equipment. Electrical connections
are, preferably, made to a single pin contact at the top of the
cartridge and to its case (ground connection).
Mechanically, the cartridge is, in one respect, screwed into the
housing. A pin at the bottom of the assembly is then mechanically
connected to pipe through the use of a mating connector, shaft, and
fluid seal of the housing. Devices according to this invention
preferably require no calibration after installation in the housing
and require no calibration downhole.
A surface interrogator, (e.g. a bridge rectifier, an electronic
diode switching bridge or their equivalents) is used in certain
embodiments to process sensor information for independent
interrogation of each sensor by surface equipment. The diode bridge
negates the need for powered downhole electronics and also permits
interrogation from the surface of both downhole sensors over a
single conductor wireline cable.
In one embodiment the present invention discloses a sensor for
measuring temperature and temperature change downhole in a wellbore
due to a coil's resistance and a coil's resistance response to
temperature change.
The present invention discloses systems for locating stuck pipe
which include, in one aspect: a shot bar; a safety sub connected to
the shot bar; a lower anchor device such as a lower magnetic anchor
or a tubular with one or more bow springs connected to the safety
sub; a sensor as described about connected to the lower anchor
device; an upper anchor device connected to the sensor; a slip
joint connected to the upper anchor device; one or more sinker bars
connected to the slip joint; a collar locator connected to the
sinker bar(s); a cable head connected to the collar locator; and a
cable extending from the cable head to a signal and/or control
system. A slip joint according to the present invention, in one
aspect, includes a housing, a mandrel, and a two conductor coil
cord assembly.
It is, therefore, an object of at least certain preferred
embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious devices, systems, and
methods for determining the location of a stuck tubular, e.g. but
not limited to a stuck pipe such as a drill string in a
borehole;
Such devices systems, and methods which provide signals indicative
of both torsional and tensional deformations;
Such devices, systems and methods which do not require downhole
powered electronics;
Such devices, systems and methods which permit independent
interrogation of multiple sensors (two or more) via a single
conductor cable;
Such devices, systems and methods with a torque sensor which is
resettable mechanically and electrically;
Such devices, systems and methods which do not require calibration
after installation;
Such devices, systems and methods which are useful to determine
temperature and temperature change downhole;
Such devices, systems including an easily replaceable cartridge
containing the sensors;
Such devices and methods for the separate and simultaneous
detection of torque and/or stretch of a tubular in a wellbore hole,
or hollow channel of another tubular; and
New, useful, unique, efficient, nonobvious slip joints.
This invention resides not in any particular individual feature,
but in the combinations of them herein disclosed and claimed and it
is distinguished from the prior art in these combinations with
their structures and functions. There have been outlined, rather
broadly, features of certain embodiments of the invention in order
that the detailed descriptions thereof that follow may be better
understood, and in order that the present contributions to the arts
may be better appreciated. There are, of course, additional
features of the invention that will be described hereinafter and
which may be in the subject matter of claims appended hereto. Those
skilled in the art will appreciate that conceptions, upon which
this disclosure is based, may readily be utilized as a basis for
the designing of other structures, methods and systems for carrying
out the purposes of the present invention. It is important,
therefore, that the claims be regarded as including any legally
equivalent constructions or steps insofar that they do not depart
from the spirit and scope of the present invention.
The present invention recognizes and addresses the
previously-mentioned problems and long-felt needs and provides a
solution to those problems and a satisfactory meeting of those
needs in its various possible embodiments and legal equivalents
thereof. To one of skill in this art who has the benefits of this
invention's realizations, teachings and disclosures, other and
further objects and advantages will be clear, as well as others
inherent therein, from the following description of
presently-preferred embodiments, given for the purpose of
disclosure, when taken in conjunction with the accompanying
drawings. Although these descriptions are detailed to insure
adequacy and aid understanding, this is not intended to prejudice
that purpose of a patent which is to claim an invention no matter
how others may later disguise it by variations in form or additions
of further improvements.
DESCRIPTION OF THE DRAWINGS
So that the manner in which the above-recited features, advantages
and objects of the invention, as well as others which will become
clear, are attained and can be understood in detail, more
particular description of the invention briefly summarized above
may be had by reference to certain embodiments thereof which are
illustrated in the appended drawings, which drawings form a part of
this specification. It is to be noted, however, that the appended
drawings illustrate certain preferred embodiments of the invention
and are therefore not to be considered limiting of its scope, for
the invention may admit to other equally effective or equivalent
embodiments.
FIG. 1 is a side view in cross-section of a tool according to the
present invention.
FIG. 2 is a perspective view of part of the tool of FIG. 1.
FIG. 3 is a cross-sectional view along line B--B of FIG. 2.
FIG. 4 is across-sectional view along the line A--A of FIG. 1.
FIG. 5 is a schematic showing steps in the assembly of the tool of
FIG. 1.
FIG. 6 is a side cross-section view of a part of a sensor of the
tool of FIG. 1.
FIG. 7 is an end view in cross-section of the sensor of FIG. 6.
FIG. 8 is an end view in cross-section of a part of a sensor of the
tool of FIG. 1.
FIG. 9 is a side cross-sectional view of the sensor of FIG. 8.
FIG. 10 is an end view of the other end of the sensor of FIG.
8.
FIG. 11 is an end view of a cap of the tool of FIG. 1.
FIG. 12 is a side cross-sectional view of the cap of FIG. 11.
FIG. 13 is a top view of a carrier of the tool of FIG. 1.
FIG. 14 is a side cross-sectional view of the carrier of FIG.
13.
FIG. 15 is an end view of an end of the carrier of FIG. 11.
FIG. 16 is a schematic view of certain components of a system
according to the present invention using a tool as in FIG. 1.
FIG. 17 is a side view partially in cross-section of a tool
according to this invention.
FIG. 18 is a side view of a tool according to this invention.
FIG. 19 is a exploded schematic view of a system according to this
invention.
FIG. 20 is a side view in cross-section of a slip joint according
to the present invention.
FIG. 21 is an enlarged view of a portion of the slip joint shown in
FIG. 20.
FIG. 22 is an enlarged view of a portion of the slip joint shown in
FIG. 20.
FIG. 23 is an enlarged view of a portion of the slip joint shown in
FIG. 20 .
DESCRIPTION OF EMBODIMENTS PREFERRED AT THE TIME OF FILING FOR THIS
PATENT
Referring now to FIG. 1, a tool T according to the present
invention has a sensor cartridge assembly A with two sensors, one
for sensing torque or torsion and one for sensing compression or
tension. The torque sensor includes a torque sensor coil 21 mounted
on a torque coil support 6 and an upper rotary sensor 8 and a lower
rotary sensor 11 with ends within the torque sensor coil 21. The
tension sensor includes a stretch sensor coil 20 mounted on a
stretch coil support 13 and a sensor core 16 partially within the
stretch sensor coil 20. A sensor shaft 14 extends through both
coils.
The two sensors operate autonomously. Torsion which affects the
upper rotary sensor 8 does not affect the tension (or "stretch")
sensor. Conversely, tension which affects the stretch sensor does
not affect the torque sensor.
As shown in FIGS. 1 and 5, the sensor cartridge assembly A has a
sensor core 16 attached to the sensor shaft 14 by a pin 7b. The
sensor shaft 14 is slotted at the opposite end and axially runs
through the center of both sensor sections. The sensor shaft 14 is
then coupled to the upper rotary sensor 8 by friction between a pin
7 installed through the upper rotary sensor 8 and between the walls
of a slot 14c in the sensor shaft 14. This slot and pin arrangement
between the sensor shaft 14 and upper rotary sensor 8 isolate the
torque sensor from axial motion, coupling only rotation of the
sensor shaft 14 to the upper rotary sensor 8.
Pipe movement, both tensional or torsional, is directed towards the
appropriate stretch or torque sensor. Axial movement of the sensor
core 16 is detected as stretch displacement by the stretch sensor
coil 20. Rotation of the upper rotary sensor 8 is detected as
torque displacement by the torque sensor coil 21.
A stretch transducer is comprised of a solenoidal coil 20 and a
moving core, part of the sensor core 16. The stretch sensor coil 20
is supported by a stretch coil support 13. Within the core of the
sensor coil 20 is one end of the sensor core 16 and one end of the
lower rotary sensor 11, separated by a small gap G. Both of these
components are, preferably, made from a permeable material. The
sensor shaft 14 that runs through the lower rotary sensor 11 and is
attached to the sensor core 16 is made, preferably, from
non-ferrous material. The lower rotary sensor 11 is, preferably,
fixed in place and not allowed to move axially. The sensor core 16,
typically attached to pipe, may move axially. This axial
displacement of the sensor core 16 modulates the inductance of the
stretch sensor coil 20 and resulting change in inductance is
measured by surface equipment. The sensor core 16, preferably
cylindrical in nature, is rotatable 360.degree. without changing
the inductance of the stretch sensor coil 20. Hence, the stretch
sensor is immune from torque applied to the pipe.
A torque transducer comprises, preferably, two permeable tubes, the
upper and lower rotary sensors 8 and 11, with slots or poles on
their facing ends placed within the core of the solenoidal torque
sensor coil 21. These pole ends are arranged so that their pole
faces overlap each other axially, but are, preferably, restrained
from touching each other, maintaining a measurable gap G between
them. Retaining rings 10a and 10b are attached to both pole pieces
so as to provide a suitable flange in which to separate the pole
pieces. Teflon.TM. washers bracket the retaining rings and are
compressed together and up against the pin face or bore flange of
the torque coil support 6 by compression springs 12a and 12b. The
torque coil support 6 also provides a base for the torque sensor
coil 21.
The upper rotary sensor 8 is "keyed" to the sensor shaft 14 and
rotates in direct relation to pipe movement. This rotation upsets
or changes the amount of overlap or area of effacement of the pole
pieces of the upper and lower rotary sensors 8 and 11 in linear
fashion and is measured as a linear change in inductance of the
torque sensor coil 21.
The lower rotary sensor 11 is held in place, prevented from
rotating over a small range of input torque rotation or moving
axially towards the stretch sensor coil 20 by the compression
spring 12a acting upon the Teflon.TM. sandwiched retaining ring
10a. An alignment pin 7a installed through the sensor shaft 14
engaged within a delta slot 11b of the lower rotary sensor 11
contacts sloping walls of the slot as normally occurs when input
torque rotation directs the alignment pin 7a to span the distance
between the walls of the delta slot 11b. Upon contact with the
walls of the delta slot by the alignment pin 7a and further input
torque rotation, the lower rotary sensor 11 is spun around its
axis, or around with the sensor shaft 14. The washers bracketing
the retaining ring 10a permit near friction-free rotation of this
pole piece in the manner described. Engagement of the alignment pin
7a with the walls of the delta slot serves to reorient or "reset"
the torque sensor. FIGS. 2 and 3 indicate the pin-slot arrangement
and the degree of movement provided thereby.
Proper alignment of the pole faces of both rotary sensor pieces is
preferred for detection of both left and right hand torque. The
delta slot 11b and alignment pin 7a limit the degree of radial
displacement of the lower rotary sensor (which "floats" with some
degree of freedom) relative to the faces of the upper rotary sensor
(the present invention, in one embodiment, limits this radial
displacement to approximately .+-. preferred 15.degree.). A typical
torque measurement begins with the pole faces oriented as shown in
FIG. 4 with the alignment pin 7a in the middle of the delta slot
11b. Rotation of the sensor core 16 rotates the upper rotary sensor
8 and the alignment pin 7a within the delta slot 11b. Rotation of
the upper rotary sensor 8 is measured as torque displacement so
long as the lower rotary sensor 11 remains stationary. Once the
alignment pin 7a engages a wall of the delta slot 11b, the upper
and lower rotary sensor pole pieces rotate together, their degree
of displacement fixed. The degree of fixed displacement is
determined by the geometry of the delta slot and the axial position
of the alignment pin within the slot. There is friction force
between the pin 7 and the slot of shaft 14. The diameter of the pin
and the dimensions of the slot feature on the end of the shaft are
preferably selected so that there is friction contact between the
members. The slotted shaft acts as a spring to maintain this
friction. This is needed to prevent "slop" in the torque
transducer. If there is slop in this area, rotation of the shaft
may not rotate the upper rotary sensor 8 until a wall of the
slotted shaft contacts pin 7 (inserted through the upper rotary
sensor 14). If contact with the wall of the slot is not achieved,
information about torque strain of a tubular member may be
lost.
Spring 12b acting upon a PTFE sandwiched snap ring 37 (installed on
the upper rotary sensor 8) forces the upper rotary sensor up
against the shoulder of the torque coil support 6. Similarly,
spring 12a acts upon the lower rotary sensor 11 to force it up
against the pin shoulder of the torque coil support 6. With both
rotary sensors forced into and held within the core of the torque
coil support there is a measurable gap between the pole faces of
each rotary sensor piece. This gap is preferably from about 5 to
about 15 thousandths of an inch (for adequate operation, the pole
faces do not touch each other). Achieving the proper gap dimensions
is accomplished by adjusting the thickness of one or more PTFE
washers that bracket the snap rings.
As shown in FIG. 1 and in Step 1 in FIG. 5, assembly of a bi-sensor
cartridge assembly B according to the present invention begins by
inserting an end of the sensor shaft 14 into a hollow end 16a of
the sensor core 16 and pinning the two together with a pin 7b. A
pin 7a is inserted into a hole 14a on the sensor shaft 14. Washers
9a and 9b, preferably made from a low friction material such as
polytetraflouroethylene (PTFE) are disposed on either side of a
collar 16c of the sensor core 16. An end 14b of the sensor shaft 14
with a slot 14c is inserted through an opening 13a into a channel
13b extending centrally through a stretch coil support 13. A
retainer cap 15 is threadedly secured to the sensor core 16 with a
portion 16b of the sensor core 16 protruding through an opening 15a
in the retainer cap 15.
The collar 16c limits possible axial movement of the sensor core 16
with respect to the retainer cap 15 and pin flange of the stretch
coil support 13, and therefore limits axial movement of the sensor
core 16 and of the sensor shaft 14 with respect to the stretch
sensor coil 20.
As shown in Step 2 of FIG. 5, the end 14b of the sensor shaft 14 is
inserted into a lower rotary sensor 11 with a central channel 11a
therethrough, a delta slot 11b at one end, and slots 11c at an end
11e. A spring 12a is inserted around the lower rotary sensor 11 and
into the stretch coil support 13 to abut an interior shoulder 13c
of the stretch coil support. A washer, 9c, preferably of PTFE is
inserted around the sensor shaft 14 and abuts the spring 12a. A
snap ring 10 installed in a groove 11d on the lower rotary sensor
11 abuts the washer 9c and the pin 7a is disposed in the delta slot
11b. A washer 9d, preferably of PTFE, abuts the snap ring 10a. The
spring 12a limits movement of the lower rotary sensor 11 with
respect to the sensor shaft 14 (to the right as viewed in FIG. 5).
The end 14b of the sensor shaft 14 is inserted into a central
channel 6a of a torque coil support 6. The end 11e of the lower
rotary sensor 11 projects into the channel 6a.
As shown in Step 3, FIG. 5, a snap ring 10b is installed in a
groove 8a on an upper rotary sensor 8. An end 8b of the upper
rotary sensor 8 with slots 8c therein is inserted through a washer
9e, preferably of PTFE, and an end 8d of the upper rotary sensor 8
is inserted into a washer 9f, preferably of PTFE. The snap ring 10b
will abut both washers 9e and 9f. The end 14b of the sensor shaft
14 is inserted through a central channel 8e extending through the
upper rotary sensor and a pin 7c through a hole 8f is disposed for
reception in and for movement in the slot 14c of the sensor shaft
14. The end 8b of the upper rotary sensor 8 is disposed adjacent
the end 11e of the lower rotary sensor 11 within the channel 6a of
the torque coil support 6. Movement of the upper rotary sensor with
respect to the sensor shaft in one direction (to the right as
viewed in FIG. 5) is limited by the bore flange of the torque coil
support 6. The only allowed axial motion of the upper rotary sensor
is to the left as viewed in FIG. 5; however, this axial motion is
prevented by the spring acting upon the PTFE sandwiched snap ring
and the assembly is forced up against the bore flange of the torque
coil support 6. A spring 12b disposed about the upper rotary sensor
8 abuts the washer 9f at one end and a shoulder 4a of an electronic
carrier 4 at the other end. The spring 12b limits movement of the
upper rotary sensor in the other direction (to the left in FIG. 5)
and helps maintain the pin 7c disposed in the slot 14c as well as
assisting in maintaining a desired gap between the end 8b of the
upper rotary sensor and the end 11e of the lower rotary sensor. The
end 14b of the sensor shaft 14, the end 8d of the upper rotary
sensor, and the spring 12b are disposed within a channel 6b of the
torque coil support 6. The electronic carrier 4 is secured to the
torque coil support 6 with a pin 5 that extends through a hole 6d
in the torque coil support and a hole 4b in the electronic carrier
4. A bridge rectifier (e.g. a diode switching bridge) 3 is disposed
in a slot 4c in the electronic carrier 4 and wires from the two
coils (see FIG. 1) go through a slot 4e to the bridge 3. A PTFE
insulated feed through terminal 1 has a pin 1a extending into the
slot 4c, a PTFE body 1b disposed in a channel 4d, and an end 1c of
the pin 1a which extends beyond the carrier 4. A cap 2 is secured
over the carrier 4 to the torque coil support 6 (e.g. by threaded
engagement).
As shown in FIG. 1, the switching bridge 3 has a positive
connection 3a, a negative connection 3b, a ground connection 3c
soldered at 3d to the carrier 4, and a connection 3e from which
extends a wire 3f to the pin 1a. An insulated wire 20b extends from
the stretch sensor coil 20, to the slot 4e, and to the positive
connection 3a. An insulated wire 21b extends from the torque sensor
coil 21, to the slot 4e, and to the negative bridge connection 3b.
A wire 3g extends from the ground connection 3c to the point 3d.
Current from a surface source (e.g. interrogating current) flows
through the assembly via the pin 1a and the wire 3f. The signal
from the surface can be AC or DC current. Use of DC current allows
for interrogation of one or more sensors. By using a plurality of
zener diodes are connected in series with a plurality of sensors,
e.g. three or more, and the zener diodes are rated at various
different increasing voltages, then each sensor can be individually
interrogated. For example, in one embodiment in which three zener
diodes are connected in parallel and rated 5 volts, 10 volts, and
15 volts respectfully, the 5 volt diode will conduct only after 5
volts is impressed across it. This same 5 volt voltage is felt
across the other zener diodes; however, the level of voltage to
"turn them on" has not been exceeded so ideally no current flows
through them. A first sensor connected in series with the 5 volt
zener diode is activated so long as 5 volts is impressed across the
zener diodes. If 15 volts or more is impressed across the parallel
connected zener diodes, all three diodes conduct current. With
three sensors connected in series with all three zener diodes
sensing is possible with all three sensors. Preferably the sensors
become passive or unchangeable after they are energized; hence, in
the configuration above after application of 5 volts to the zener
diodes the first sensor provide information about itself through
the zener diode rated at five volts and then ceases to become
active upon the application of higher voltages. After application
of 10 volts, two sensors are seen, but one has ceased to become
active; therefore, only the 10 volt sensor is detected and then
also becomes passive or ceases to be active. The process repeats
for the 15 volt zener diode.
FIG. 4 depicts an axial view of both rotary sensor pole pieces
imposed on each other. Each sensor pole piece end within the torque
sensor coil has one or more indented areas. Several indented areas
result in a "fingered" sensor pole piece end. As shown the upper
rotary sensor's pole piece end within the torque sensor coil has
four fingers 50 and the lower rotary sensor's pole piece end within
the torque sensor coil has four fingers 52. The faces of the
fingers of the rotary sensors' pole pieces are crosshatched
differently to clarify the area of overlap between the rotary
sensor pieces. Because of the arrangement of the pole pieces, right
or left hand torque rotation is discernable. In this embodiment,
right hand sense rotation enlarges the area of finger effacement
and is measured as an increase in inductance of the torque sensor
coil 21; and conversely, left hand sense rotation decreases the
area of finger effacement and is measured as a decrease in
inductance of the torque sensor coil 21. The change in area is
linearly proportional to input torque rotation; hence, the change
in inductance of the torque sensor coil 21 is linear.
Sensitivity of the torque sensor can be increased by increasing the
number of fingers or poles that efface each other. With one finger
on each pole piece, i.e. with the two semicircles that efface each
other, the semicircles can form a circle or a semicircle as one is
rotated with respect to the other. They rotate exactly 180.degree.
from no effacement to full effacement. If each semicircle is split
into two components (like slices of pie) and symmetrically arranged
to form a circle or four pieces of a pie, there is no effacement of
any of the slices (total of four). Rotation of two symmetrical
slices against the other two slices result in more overlap of the
areas and full effacement after 90.degree. of rotation. Thus there
is a linear relationship between the number of poles and degree of
maximum rotation between no effacement to full effacement. This
translates into increased sensitivity to pipe rotation. The
relationship between maximum torque measurement and number of poles
is:
One embodiment of the present invention employs four fingers or
poles on each rotary sensor piece. Hence, 360.degree. divided by a
total of eight pole pieces equals a maximum sensing range of
45.degree. (or .+-.22.5.degree.). Doubling the number of pole
pieces of this embodiment of the present invention results in a
maximum sensing range of 22.5.degree., and so forth. The same
inductance value is reached for the full effacement of a two pole
system as it will for an eight pole system of any other number of
poles; conversely, the same inductance value will be reached for no
effacement of any number of symmetrically arranged poles.
The sensor core 16 and the sensor shaft 14 are permitted to move
axially (left-to-right as viewed in FIG. 1) to the extent permitted
by the open area around the collar 16c. Movement of the sensor core
16 in the stretch sensor coil 20 changes the coil's inductance.
Inductance of the stretch sensor coil is inversely proportional to
the length of gap G between the sensor core 16 and one end of the
lower rotary sensor 11 (end containing delta slot feature 11b). A
smaller gap means a larger coil inductance and vice versa. Axial
movement of the sensor core 16 from left-to-right as viewed in FIG.
1 is referred to as "Stretch or Tension measurement" and would be
measured as a decrease in coil inductance as the length of the gap
G is increased. Such movement of the sensor core is isolated from
the upper rotary sensor 8 and the lower rotary sensor 11 since
there is no connection between the sensor core 16 and the upper and
lower rotary sensors as previously described and no connection
between the sensor shaft 14 and the upper and lower rotary sensors
that prevents the limited axial movement; i.e. when the sensor core
16 moves axially (to the limited extend allowed) the upper and
lower rotary sensors do not move axially. For the embodiment shown
the gap G ranges between one sixteenth and one eighth inches and is
most preferably maintained at three thirty secondths of an
inch.
The upper rotary sensor 8, with its ends 8b is free to move
radially with respect to the lower rotary sensor 11; the effacement
area of the sensor ends co-act to alter the inductance of the
torque sensor coil 21. The upper rotary sensor rotationally moves
with the sensor shaft 14 (and sensor core 16) due to the co-action
of the pin 7c and the slot 14c previously described. Such rotation
of the rotary sensor does not alter the inductance of the stretch
sensor coil due to the cylindrical design of the sensor core 16 and
the physical separation of the stretch and torque sensor coils.
The torque sensor is "reset" with the aid of the delta slot 11b and
alignment pin 7a. By axially stroking the sensor core 16 (i.e., by
mechanically lowering and raising a wireline cable attached to a
freepoint string of tools), thereby stroking the alignment pin 7a
within the delta slot 11b, the lower rotary sensor 11 rotates
towards a neutral or starting point (as shown in FIG. 3) as the pin
7a engages a wall of the delta slot 11b. Alternatively, the
alignment pin 7a can remain stationary and the lower rotary sensor
can be stroked toward the stretch sensor section. Again, the delta
slot 11b will contact the alignment pin 7a and rotate the lower
rotary sensor 11 towards neutral. ("Neutral" means a mid-range
position relative to the overall torque limit. A mid-range position
in the present invention implies that after the completion of a
resetting operation, performed electrically or mechanically, the
alignment pin 7a will be positioned along an axial line drawn
through the apex of the delta slot 11b.) Axial stroking of the
lower rotary sensor 11 requires the force of a compression spring
12a to be overcome.
The stretch sensor coil 20 provides sufficient electromagnetic
force to reset the torque sensor by moving the lower rotary sensor
11 into the stretch sensor coil 20 and is electrically energized
from surface equipment (not shown). Upon the electromagnetic
engagement of the stretch sensor coil 20 by surface equipment, a
small separation between the sensor core 16 and lower rotary sensor
11 within the core of the stretch sensor coil 20 is reduced as the
lower rotary sensor is magnetically attracted towards the fixed
sensor core 16. This attractive force between the sensor core 16
and the end of the lower rotary sensor 11 is of sufficient strength
to compress the coil spring 12a and allow the lower rotary sensor
11 to be stroked, forcing the delta slot 11b against the alignment
pin 7a. This reorients the lower rotary sensor 11 with respect to
the upper rotary sensor 8 (rotates towards neutral). The reset
operation is completed when energizing current is removed from the
stretch sensor coil 20, thereby allowing the compression spring 12a
to axially return the properly aligned lower rotary sensor 11 up
against the pin flange of the torque coil support 6, reestablishing
the same measurable gap G between the upper and lower rotary sensor
pole pieces.
The present invention provides for a mechanical and an electrical
means to reset the torque transducer. The device (or freepoint
tool) can be reset from the surface by either manually stroking the
device or by the electromagnetic engagement of the stretch sensor
coil 20. The stretch sensor is mechanically reset. Procedurally,
the sensor core 16 is stroked to either end of its allowed
displacement. In one typical application, a wireline string of
tools is lowered in the well and by this action moves the sensor
core 16 further into the core of the stretch sensor coil 20 to a
fixed reference point. The device is prepared to measure stretch of
pipe as it is tensionally strained from the surface. Conversely,
the freepoint string is raised by the wireline thereby moving the
sensor core 16 to its other extreme end permitting measurement of
compression of pipe.
Both sensors may be passively interrogated by surface equipment
over a single conductor wireline cable, without the need for a
downhole oscillator or any other actively powered downhole
electronics. A simple switching diode bridge 3 incorporated into
the cartridge, operates in synchronous fashion with diode switches
contained in a surface located freepoint receiver. This electronic
switching technique permits the separate and simultaneous
discrimination of torque and stretch transducer signals from
surface equipment, and is schematically represented in FIG. 16. The
signal applied at the surface can be bipolar (an AC signal) or
unipolar (a DC pulse) and these signals may be generated by a
variety of equipment which is not limited to only alternating
current signal generators. Other equipment that may be used
includes a pulse generator or a variable DC power supply.
As shown in FIG. 16, with proper surface signal excitation of the
downhole tools, discrete diodes within the switching diode bridge 3
are either turned on or off, like a switch. Assuming a fixed
positive voltage, with respect to chassis ground, is applied to the
wireline, a current, I1, flows from the signal generator, through
the load resistor, down the wireline, through a "forward biased"
diode D1, through the stretch sensor coil, and then back to the
signal generator through the ground leg or armor of a wireline
cable. Changes in the inductance of the stretch sensor coil alter
the amount of current flow through the wireline and the amount of
current flow is monitored at the surface through another switching
diode D5, since this diode is also forward biased with respect to
ground.
A measurable direct current voltage is then available from the
cathode of diode D5 that varies in direct proportion to the amount
of current flow allowed by the stretch sensor coil. Information is
then displayed about stretch displacement on analog meters, digital
panel meters, or is "quantized" for use in a digital acquisition
system after filtering and amplification of the stretch detected
voltage. Similarly, information about the torque sensor is obtained
by reversing the voltage imparted on the wireline by the signal
generator. With a negatively swinging voltage applied to the
wireline, a current I2, flows in a direction opposite of current I1
through biased diode D2. A measurable direct current voltage is
then available from the cathode of D6. This voltage varies in
direct proportion to the amount of current flow, I2, allowed by the
torque sensor coil. Pipe movement, either torsional or tensional,
is transmitted to an appropriate torque or stretch sensor
section.
As shown in FIGS. 17 and 18 cartridge 100 according to the present
invention as shown in FIGS. 17 and 18 (like the assembly A, FIG. 1)
is installed into a properly bored and threaded freepoint tool
housing 102. This body or housing 102 accommodates the cartridge
100 by providing physical protection from well bore fluids and the
apparatus to transmit mechanical movement of pipe in the wellbore
to be examined to the cartridge 100. The cartridge 100 is inserted
into the housing 102 until its sensor core 103 (like the sensor
core 16) mates with a press fit with a mandrel connector 104
attached to the end of a mandrel shaft 105 running through the
housing 102. The cartridge 100 is then retained in place by a
belleville washer 106 and locknut 107. Installation of a feed-thru
connector 108 (like the terminal 1) and an upper sub 109 completes
the assembly of the tool. The upper sub 109 has an O-ring seal 133
which seals the tool's interior from the outside environment. The
mandrel shaft 105 extends through a flexible fluid seal 110 and a
fluid seal block 111. A protective shield 112 shields the seal and
seal block Once connected to the sensor core extending from the
cartridge assembly 100, the mandrel shaft 105 moves as the sensor
core moves (e.g. typically with a one-fourth inch stroke and most
preferably with a one-sixteenth inch stroke and with rotation
through a full three hundred and sixty degrees). No calibration of
the assembled tool is required. A collar 117 at the bottom of the
mandrel 105 in combination with the mandrel connection 104 serves
to retain the mandrel within the housing. In one embodiment
measurement of stretch of about 0.020 inches is sufficient for an
indication of tension on a tubular. A stroke of 0.030 inches is
more than adequate for such a tool. Once the tool is assembled,
turning the cartridge assembly forces the sensor core 16 into the
mandrel connector 104 and then backing the cartridge assembly out
of the housing one and one half turns correctly positions the
sensor core 16. Preferably the tool is filled with silicon oil
before the upper sub is installed.
FIG. 19 illustrates a system 300 according to the present invention
which includes a tool 302 like the cartridge/housing device of
FIGS. 17 and 18. Beneath the tool 302 a lower magnetic anchor 304
for anchoring the tool 302 to a pipe's interior (or a lower bow
spring 303) may be used. A safety sub 306 is connected to the lower
magnetic anchor 304 (or lower bow spring 303) to serve as a
connector for a conventional shot bar 308 which is used to jar a
joint loose for a typical backoff operation. A backoff operation is
the purposeful detonation of explosive prima-cord by a blasting cap
to jar a tubular connection free. Prior to detonation, left hand
torque (or right hand torque for left handed pipe) is put into the
connection and weight is set (at the block) such that the tubular
is neutral (not in tension or compression, slight tension is
allowed and at times maybe preferable) at the connection to be
unscrewed. Ignition of the prima-cord jars the connection and the
joint spins free due to the backoff torque previously put into the
tubular connection. A backoff operation is completed by unscrewing
the connection and separating the string from another member, e.g.
a fish, left in the hole.
Immediately above the tool 302 is connected an upper magnetic
anchor 312 for anchoring the tool 302 within a tubular such as a
stuck pipe (or an upper bow spring 311 is used). A slip joint 314
is connected to the upper magnetic anchor 312 (or upper bow spring
311) to provide play in the tool string to allow a wireline therein
to "float" without snapping and allows the tool 302 to be
stabilized below the slip joint, allowing the wireline to float
above the slip joint. Preferably two electrical circuits are
provided through the slip joint 314 by a two conductor coil cord
assembly with integrated coaxial connectors at each end, providing
a core (center pin) and a ground (return) electrical connection
between each end (i.e. pin of one connector to pin of the other
connector, ground side of one connector to ground side of the other
connector). It is preferable to physically connect the sliding
members of the slip joint 314, (a mandrel and housing) by an
electrical wire connection rather than depend upon friction contact
between the two sliding components to provide a reliable ground
connection. Furthermore, use of integrated connections on the coil
cord assembly permit quick replacement of the component in field
operations and also ensures a more positive connection sealing out
well fluids from the electrical circuits contained within the
assembly. One or more sinker bars 316 are used in the tool string
as needed and a conventional collar locator 318 is used to locate
joint collars to properly locate the tool 302. A conventional cable
head 322 connected to the collar locator provides a mechanical
attachment between a wireline 324 and the tool 302. The wireline
324 may be a conventional single conductor wireline cable extending
down to the tool 2302 through the various interconnected parts of
the tool string and to a surface control and signal system 326
which sends interrogating signals down to the tool 302; receives
and records signal responses from the tool 302; displays tool
depth, system status. A freepoint receiver may display tool depth,
system status (i.e. freepoint operation, collar logging, or backoff
operation in progress, power supply failure, calibration in
progress, etc), time, date, provide hard copy outputs of freepoint
readings, provide a hard copy output of a collar log, store all
measurements on magnetic media for storage and retrieval purposes,
and so forth. Preferably two connections at the slip joint include:
a connection for the primary signal path and a connection for
ground return to insure a good circuit for the signal from the
sensor core to the signal system 326.
Due to the relationship between changes in electrical resistance of
a conductor such as a wire in response to changes in temperature,
the coils used in the present invention may be employed to measure
temperature and temperature change downhole in a wellbore. Over a
moderate temperature range (e.g. 100.degree. C.), the change in
resistance of either sensor coil will be proportional to the change
in temperature at a downhole location. Temperature at a downhole
location (T2) is referenced to some other known temperature (T1) at
which a proportionality constant (a.sub.t1) has been experimentally
obtained for the material used in the coil windings, and where a
known resistance (R.sub.t1) was obtained for the coil windings. As
downhole coil resistance (R.sub.t2) is monitored, downhole
temperature can be calculated from the relationship:
For extended temperature ranges (greater than 100.degree. C.) the
relationship above may be modified to account for non-linear
changes in the material properties of the coil windings. In
general, the technique to measure temperature over extended ranges
is the same as the linear model shown above to compute downhole
temperatures from a coil resistance. Either coil (or both) shown in
FIG. 1 may be interrogated to produce a signal indicative of
temperature.
Referring now to FIGS. 20-23, a slip joint 400 according to this
invention has a housing 401, a mandrel 402, and a two conductor
coil cord assembly 433 with both the mandrel and the cord assembly
movable from end to end in the housing.
The housing 401 is approximately four feet long in one preferred
embodiment and is threaded at each end to accept a pin connection.
The housing 401 is slotted throughout its length with slots 434 to
allow easy flow of well fluids through its inner chamber. In one
embodiment there are six rows of fourteen slots radially spaced
about 60.degree. apart with slots approximately 11/2 inches long.
Each row of slots is preferably offset from the other to preserve
strength in the housing 401.
The mandrel 402 operates within the housing 401 and is prevented
from being extracted from the housing 401 by the abudment of a
mandrel bushing 405 (screwed unto the mandrel 402 and retained by a
set screw 420 up against a pin flange 421 of a keyway sub 406.
Conversely, the mandrel 402 collapses into the housing 401 until a
keyway locknut 407 and a locknut 408 make contact. The mandrel 402
is prevented from rotating within the housing 401 by a pin or key
409 that rides within a milled region of the mandrel 402 and keyway
sub 406. This arrangement allows only lineal stroking of the
mandrel 402 within the housing 401. This rotational restriction
prevents undesired coiling up or uncoiling of the two conductor
coil cord assembly 433. One end of the mandrel is grooved to accept
an O-ring seal 422 and is threaded into a pin sub 416, sealing out
well fluids from entering the inner bore of the mandrel 402. The
other end of the mandrel 432 is machined to accept one end 422 of
the two conductor coil cord assembly 433 and is also sealed from
well bore fluids by an o-ring seal 423.
The two conductor coil cord assembly 433 consists of a two
conductor coil cord 403 integrated with fluid seal connectors 404
and 424 at its ends. The mandrel 402 and coil cord assembly are
free to stroke within the housing 401 over a desired length, e.g.
in one embodiment a length of approximately 20 inches The two
conductor coil cord assembly 433 in combination with other
electrically conductive components provides for two separate
electrical circuits through the Slip joint assembly or tool.
The primary or core electrical circuit path begins with a banana
plug 411 and an insert 412 located within a box sub 414. An
insulator 413 supports the insert/banana plug assembly as well as
providing electrical isolation from the box sub 414. The core or
center connection 438 (e.g. a metallic pin) of the fluid seal
connector 404 mates with the insert 412. The primary circuit
continues through the coil cord assembly to a core connection 439
of the other fluid seal connector 424. A pin contact 415 mates with
the center contact of the fluid seal connector 424 and with one end
of a contact rod 410. The contact rod 410 is, preferably, sleeved
with PTFE tubing (not shown) to electrically isolate the primary
circuit from the mandrel 402. The contact rod 410 is soldered to an
insert 419 located within the pin sub 416 which provides for
electrical connection to other freepoint tool components (e.g. by a
banana plug within a mating box connection). An insulator 417
supports the insert and provides electrical isolation from the pin
sub 416. The insert 419 is retained in the insulator 417 by a
spirol pin 418.
A secondary electrical pathway, or ground (return) leg, is from the
box sub 414 to the mandrel 402. Connection between the box sub 414
and mandrel 402 is provided by one wire of the two conductor coil
cord assembly 433. This pathway is from the fluid seal connector
404 through the coil cord 403 and to the other fluid seal connector
424. The shell of each fluid seal connector mates with the box sub
or mandrel by a threaded connection with integrated O-ring seals
423 and 441 to prevent entrance of well fluids into the mating
connections. This method of providing a physical and an electrical
connection between the sliding members of slip joint ensures a
positive and secure ground connection, rather than depend upon
friction contact between the mandrel 402, pin or key 409, and
housing 401.
In conclusion, therefore, it is seen that the present invention and
the embodiments disclosed herein and those covered by the appended
claims are well adapted to carry out the objectives and obtain the
ends set forth. Certain changes can be made in the described and in
the claimed subject matter without departing from the spirit and
the scope of this invention. It is realized that changes are
possible within the scope of this invention and it is further
intended that each element or step recited in any of the following
claims is to be understood as referring to all equivalent elements
or steps. The following claims are intended to cover the invention
as broadly as legally possible in whatever form its principles may
be utilized.
* * * * *